1. The molecular weight of commercially pure bicarbonate of potash, in crystals, being 100, whilst that of absolute acetic acid is 60, it is evident that every ten grains of the bicarbonate will exactly equal 6 grains of the acid. To apply this practically, we have only to exactly neutralise 100 gr. of the vinegar or solution under examination with the bicarbonate, observing the usual precautions; then, as 10 is to 6, so is the number of grains used, to the per-centage strength required. In this, as in other like cases, it is convenient to form a test-solution with the bicarbonate, by dissolving it in sufficient water to fill the 100 divisions of any simple form of ‘acidimeter,’ as _a_, _b_, or _c_; when the quantity of the solution, and, consequently, of the salt used, may be read off at once from the graduated portion of the tube. Still greater accuracy may be obtained by dissolving the bicarbonate in exactly 1000 gr. of distilled water contained in a ‘Schuster’s alkalimeter,’ previously very carefully weighed; in which case each grain of the test-solution will indicate 1/10th of a grain, or 0·1% of absolute acetic acid, whilst every 10 grains will be equal to 1 grain, or 1%. [Illustration] The test-solution may also be prepared from bicarbonate of soda, or from the carbonates of soda or potash, care being taken that the quantity of the salt dissolved be in proportion to its molecular weight. 2. (Brande.) A small piece of white marble, clean and dry, is weighed, and then suspended by a silk thread in a weighed sample (say 100 or 1000 grs.) of the vinegar or acid under examination; the action being promoted by occasionally stirring the liquid with a glass rod, until the whole of the acid is saturated, as shown by no further action on the marble being observable on close inspection. The marble is then withdrawn, washed in distilled water, dried and weighed. The loss in weight which it has sustained will be nearly equal to the acetic acid present, or strictly, as 50 (marble) to 60 (absolute acetic acid). The only precautions required are, to avoid striking the piece of marble with the rod whilst stirring the solution, or causing loss of substance in it after its withdrawal; and to allow ample time for the action of the acid on it. If the sample consists of strong acid, it should be diluted with twice or thrice its weight of water before suspending the marble in it.